1. Field of the Invention
The present invention relates to the display, by projection on a screen, of an image managed by a computer system and to the introduction or input of data into the data-processing system by the shifting of a location marker in relation to the screen.
The devices used for screen display and the devices for the input of data elements by the shifting of a pointer on the screen are often associated as peripherals of a data-processing system.
2. Description of the Prior Art
Thus, there are known work stations connected to a data-processing system that are equipped firstly with a display screen and secondly with an alphanumerical keyboard with mouse, joystick or trackball, or with a touch screen. The data elements coming from the data input device are processed by the data-processing system so as to be shown in a particular form in the image displayed in order to provide the operator with a visual check on the operation of the data input device.
Data input devices are classified into two types depending on the distance between them and the display device.
They may be close to the display device, like the touch screen which is superimposed on the display screen. Their drawbacks then are that they have a size of the same magnitude as the image, they lower the quality of the image by causing reflections and a decrease in luminosity and they cannot be used at a distance from the screen.
They may be at a distance from the display device as is the case with an alphanumerical keyboard, a mouse, a joystick or a trackball. Their drawbacks then are that they are bulky, mechanically complicated and require a link, for the transmission of the data entered, that is often a electrical wire link. Furthermore, the data element entered depends on only two or three positioning parameters such as the position of the finger in the plane of the alphanumerical keyboard, the position of the mouse in its plane of maneuvering or the angular position of the handle of a joystick.